The use of a mobile paving machine to deposit and distribute a surfacing material such as hot asphalt mix over a surface is known. These paving machines (‘pavers’) use a material distribution apparatus in the form of auger flights or paddles mounted on rotatable shafts to distribute the hot asphalt mix across a width of the surface. Traditionally the width of the auger is manually altered to accommodate different widths of surface by addition or removal of bolt-on auger sections to create wider or narrower widths.
It is a well known and generally recognised industry fact that in order to have a long lasting, consistent and homogenous asphalt surface that there must be an even and consistent “head of material” across the full width of the paving machine screed at all times. Failure to do this will lead to segregation of hot asphalt mix, an uneven finished surface and inconsistent density of the asphalt leading to reduced pavement life. Without extensions to the auger's there is a need to manually hand shovel out the hot asphalt mix to the end gates. Not only is this a hard, physically demanding task, it also causes the paving thickness/density to be compromised in this area by not having the same consistent forces acting on the screed as you would with auger guards and extensions fitted.
A fundamental and important aspect in achieving an even and consistent head of material over the entire width of the paver screed is to use auger guards and auger extensions to distribute the material generally to within 17-18″ of the respective right and left end gates. The problem frequently occurs that many roads to be paved are of varying width and require frequent paving width adjustments on the go. The paving machine must be stopped and bolt on augers and mainframe extensions added or removed as required which takes a lot of time and is not efficient or practical. It would normally take at least 15-20 minutes per side to remove or fit short auger extensions that don't require an outer support bearing. Such stops or delays also result in settling of the pavers screed on to the fresh asphalt surface being paved, causing a bump or dip in the surface.
A further disadvantage associated with manual auger extensions is that most asphalt paving crews will generally default to determining the minimum paving width required and only put on enough auger and mainframe extensions to cope with this. This in turn compromise's the head of material each time they have to extend to a wide width, resulting in an inconsistent and poor finish to the paved surface.
A smaller head of material than required reduces the forces acting against the screed which will cause the screed to drop and pave thinner than desired. Conversely the opposite is also true-by not confining the material with the correct auger extensions and guards, it is necessary to “overload” the material in an attempt to force the paving material out to the screed end gates when there is a wide width to be paved. This causes more resistance and therefore the screed will tend to rise and lay thicker than the required paving depth.
In addition, attempting to pave wide without the necessary auger extensions and guards fitted can often result in the paver getting stuck and loosing traction as a result of having a massively overloaded head of material between the tractor and the screed because there is no confinement or “tunnel” created. Effectively the paving machine is trying to drag far more material than is needed to pave but it has no choice but to try and pull this excess material in order to get enough mix out to the ends of the screed. This is a known and common problem that reduces the quality of the finished paved surface. Many people seem to accept it as being inevitable.
Furthermore, if one “confines” the head of material by using the appropriate auger extensions and guards, there will be a significantly reduced pile of material at the end of each paving run which is required to be picked up versus paving the same width run without the necessary auger extensions and guards. This saves time and effort by the crew who only need to shovel up the minimum amount of excess asphalt mix necessary.
The use of a variable width material distribution apparatus to accommodate different widths of surface, while making a pass of the paving machine over the surface, has gone some way to solving the above disadvantages. U.S. Pat. No. 4,749,304 discloses a variable width distribution apparatus comprising telescoping distribution tubes which fit over one another and connect to one another via tongue and groove interconnections to form a continuous auger worm in a retracted position and a half-worm in an extended position. U.S. Pat. No. 4,772,156 discloses this aspect more fully and improves maintenance of the auger by including a bolt-on means for replacing the individual flight elements of the distribution tubes.
The disadvantage of this arrangement is impaired efficiency of distribution of the road surfacing material in extended positions in comparison to retracted positions. In addition, while replacement of individual flight elements goes some way towards improving maintenance of the material distribution apparatus, damage to the distribution tubes themselves would still require relatively costly repair with the result that the paving machine would be out of action for a significant period.
As the hot asphalt mixture is hot, sticky and hardens when cooled, the material distribution apparatus must also be robust and able to operate over extended periods.
It is an object of the present invention to provide an improved variable width material distribution apparatus or at least to provide the public with a useful choice.
All references, including any patents or patent applications, cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinence of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein; this reference does not constitute an admission that any of these documents forms part of the common general knowledge in the art, in New Zealand or in any other country
It is acknowledged that the term ‘comprise’ may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term ‘comprise’ shall have an inclusive meaning—i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term ‘comprised’ or ‘comprising’ is used in relation to one or more steps in a method or process.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.